containerization/vminitd/Sources/VminitdCore/IOCloser.swift

//===----------------------------------------------------------------------===//
// Copyright © 2026 Apple Inc. and the Containerization project authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//===----------------------------------------------------------------------===//

#if os(Linux)

import ContainerizationOS
import Foundation

protocol IOCloser: Sendable {
    var fileDescriptor: Int32 { get }

    func close() throws
}

struct UnownedIOCloser: IOCloser {
    private let inner: IOCloser

    var fileDescriptor: Int32 { inner.fileDescriptor }

    init(_ inner: IOCloser) {
        self.inner = inner
    }

    func close() throws {}
}

/// [Nucleic vendored patch] Owns a `dup(2)` of another descriptor. Epoll keys registrations
/// on the fd NUMBER, so two IOPairs sharing one underlying file (TerminalIO: the stdout
/// relay reads the terminal fd, the stdin relay writes it) collide the moment the stdin
/// side needs an EPOLLOUT backpressure registration on the number the stdout side already
/// registered — which now fails fast (EEXIST) and killed the stdin relay. A dup shares the
/// open file description but has its own number, so each relay registers independently; the
/// description stays valid until every descriptor over it is closed.
struct DupIOCloser: IOCloser {
    let fileDescriptor: Int32

    init(duplicating fd: Int32) throws {
        let duplicate = dup(fd)
        guard duplicate != -1 else { throw POSIXError.fromErrno() }
        self.fileDescriptor = duplicate
    }

    func close() throws {
        guard Foundation.close(fileDescriptor) == 0 else { throw POSIXError.fromErrno() }
    }
}

#endif